1. Field of the Invention
The present invention is directed to a cutting device for use in an electric shaver, and more particularly to a set of an outer cutter and a plurality of inner cutter blades all made of like material having improved surface hardness.
2. Disclosure of the Prior Art
In the past, martensite stainless steels or precipitation-hardening stainless steels have been used for blades of cutting tools such as electric shavers or hair clippers. Those steels exhibit excellent mechanical toughness and shockproof, although, the surface hardness and wear resistance of the steels are not always enough to provide the cutting tools having an extended service life. In addition, when the stainless steels are polished to form blades of the cutting tools, there is a problem that burrs occur at the cutting edges of the blades. As shown in FIG. 9, as a blade angle .theta. defined between a top face 2 and side face 4 of a blade 1 is smaller, the occurrence of burrs 5 increases. Therefore, the burrs must be removed from the cutting edges after the polishing step. However, since the cutting edges often receive damages during the removing step of the burrs, it is difficult to make the cutting edge sharp.
To improve this problem, it is proposed to use ceramic materials such as aluminum oxide (Al.sub.2 O.sub.3) or zirconium oxide (ZrO.sub.2) of excellent hardness and wear resistance. However, there is another problem that the mechanical toughness of the ceramic materials is much lower than that of the steels. In addition, it is not easy to machine the ceramic materials to various shapes of the cutting tools.